Among the many types of organic compounds that have been used as insecticides, very little attention has been paid to aldehydes. The only aldehyde that has received thorough investigation is acetaldehyde (ethanal). Studies involving acetaldehyde gas are reported by Aharoni, Y., et al., in "Acetaldehyde--a Potential Fumigant for Control of the Green Peach Aphid on Harvested Head Lettuce," J. Econ. Entomol. 72(4):493-5 (1979), by Aharoni, Y., et al., in "Thrips Mortality and Strawberry Quality after Vacuum Fumigation with Acetaldehyde or Ethyl Formate," J. Amer. Hort. Sci. 105(6):926-929 (1980), and by Stewart, J. K., et al., in "Acetaldehyde Fumigation at Reduced Pressures to Control the Green Peach Aphid on Wrapped and Packed Head Lettuce," J. Econ. Entomol. 73(1):148-152 (1980). Various exposure periods were used in these studies, with various reduced pressures in the latter two studies, and the results show activity but no clear trend in data nor statistical difference between treatments at different pressures. The use of acetaldehyde as a commercial fumigant was not pursued further.
Insecticidal studies with aldehydes of three or more carbon atoms are few and inconclusive. Ferguson, J., et al., "The Toxicity of Vapours to the Grain Weevil," Ann. Appl. Biol., 35:532-550 (1948), tested 94 compounds differing widely in structure, four of which were aldehydes, in exposures of five hours at 25.degree. C. and atmospheric pressure. A screening study by Hinman, F. G., "Screening tests of compounds as fumigants for eggs and larvae of the oriental fruit fly," J. Econ. Entomol. 47(4):549-556 (1954) covered 189 compounds, one of which was propanal, which was not considered a promising candidate for further study. The same investigator participated in a second screening study, reported by Burditt, A. K., et al., "Screening of Fumigants for Toxicity to Eggs and Larvae of the Oriental Fruit Fly and Mediterranean Fruit Fly," J. Econ. Entomol. 56(3):261-265 (1963), where acetaldehyde, butyraldehyde, and isobutyraldehyde were included among 108 compounds screened, without including propanal. Exposure times were two hours at 75.degree. F. (approximately 25.degree. C.) and atmospheric pressure.
No further studies were reported on the use of aldehydes as insecticides, apparently because the low-to-moderate toxicity that the aldehydes demonstrated in these studies rendered them too weak for commercial utility. Furthermore, none of these published studies involved tests performed in the presence of an agricultural crop.
Of further potential relevance to this invention is prior art on applying gaseous fumigants under partial vacuum. An early study was reported by Sasscer, E. R., et al., "A method for fumigating seeds," U.S.D.A. Bull. No. 186: 1-6 (1915). The effect of vacuum can vary dramatically, however, with some compounds displaying increased potency under vacuum (Bhambhani, H. J., "Recent advances in vacuum fumigation," Wld. Rev. Pest Control, 3:53-56 (1964), others decreased potency (Monro, H. A. U., et al., "The influence of vapor pressure of different fumigants on the mortality of two stored product insects in vacuum fumigation," J. Stored Prod. Res. 1:207-222(1966), and still others no difference in potency (Aharoni, Y, et al., 1980, cited above). The advantage of vacuum fumigation as reported by the prior art is its effect in increasing penetration of a pesticide into a dense load (Monro, H. A. U., "Vacuum Fumigation" in Manual of fumigation for insect control, 2d edition, FAO, Rome, 1969; and Stewart, J. K., et al., cited above), such as densely packed dates (Brown, W. B. and Heuser, S. G., "Behaviour of fumigants during vacuum fumigation: I. Penetration of methyl bromide into boxes of dates," J. Sci. Food Agric. 4:48-57 (1953)), rather than achieving an increase in potency of a pesticide in an otherwise empty container.